Most conventional carpets comprise a primary backing with yarn tufts in the form of cut or uncut loops extending upwardly from the backing to form a pile surface. In the case of tufted carpets, the yarn is inserted into a primary backing by tufting needles and then a pre-coat or binder is applied thereto. In the case of non-tufted or bonded pile carpets, the fibers are embedded and held in place by a binder composition.
In both cases, the carpet construction usually also includes a secondary backing bonded to the primary backing. The secondary backing can provide extra padding to the carpet, absorb noise, add dimensional stability and often function as a heat insulator. The secondary backing, typically either a foam sheet or a woven fabric, is laminated to the primary backing by a binder composition applied to the tuft-lock coated primary backing or applied directly to the secondary backing. Similar techniques are used in the preparation of broadloom carpet as well as carpet tiles.
The physical properties of the binder are important to successful utilization as a carpet backing coating. In this regard, there are a number of requirements that must be met by such a coating. It must be capable of being applied to the carpet and dried using the processes and equipment conventionally employed in the carpet industry. It must provide excellent adhesion to the pile fibers to secure them firmly to the backing, both in tufted and non-tufted constructions. The coating must also have low smoke density values and high flame retardant properties and must accept a high loading of traditional fillers such as calcium carbonate, aluminum trihydrate, barite and feldspar. Furthermore, the coating must maintain sufficient softness and flexibility, even with high filler loading or at low temperature, to enable the carpet, if prepared in broadloom form, to be easily rolled and unrolled during installation. The softness and flexibility properties will vary depending on the style of carpet but, in all cases, it is important that the carpet will lie flat and not exhibit a tendency to curl or dome.
In the application of the coating composition to a carpet substrate, it is often advantageous to froth or foam the coating composition with a gas, typically air, before application. The gas is incorporated into the coating composition by mechanical action (frothing) to form a froth. A coating composition froths well if the desired compound froth density or air content can be obtained quickly and reproducibly. In preparing the frothed coating composition, the typical process involves mixing all the components and then incorporating the gas into the mixture using mixing equipment. Surfactants can be added to the coating composition to modify the rate and extent to which air is entrapped. Examples of such surfactants include sodium lauryl sulfate or ammonium lauryl sulfate.
Frothing of the coating composition aids in coat weight control. It is important that the froth collapse after application of the coating composition, but before drying of the coating is complete. This collapse is necessary to obtain good binding to the secondary backing. If the froth does not collapse sufficiently a froth structure remains that can have much poorer secondary backing adhesion.
It would be desirable to have a coating composition for use in the manufacture of carpet and carpet tile, such that the coating composition would froth or foam well, be sufficiently stable to obtain good coating weight control, and collapse well at some point after coating or early in the drying process (before voids are set in place by the dried compound).